Osteoporosis and bone tumors are two of the most frequent diseases of the spine, in particular of the vertebral bodies. A symptom of the diseases is inter alia a decreasing bone strength, which results in a premature degeneration of the vertebral bodies and thus results in a high risk of bone fractures for the patients.
Thanks to modern medicine there are, at least in the industrialized countries, an ever increasing number of old people. The number of cases in which vertebral fractures are discovered in patients is rising rapidly on account of this development. For example, osteoporosis is one of the most frequently encountered diseases in Japan and it is estimated that 12 million people are affected there. Since the average age of the population is currently increasing in all the industrialized nations, the number of disease cases is expected to rise even further in future.
Early detection of osteoporosis or of bone tumors is of great importance since with early treatment the risk of bone fractures can be significantly reduced and the quality of life of the persons affected can be decisively enhanced thereby. Although damage which has already occurred is often irreversible, an early medication-based treatment for example in the case of osteoporosis can prevent further bone fractures. Osteoporosis is by far the most frequent cause of fractures of the vertebral bodies.
Early detection of fractures or cracks in the vertebral bodies is however difficult because the causative illnesses often do not develop symptomatically. For this reason, changes in the bone tissue which could result in fractures are often only discovered when the spinal column is being examined radiologically for other reasons.
There is moreover as yet no consensus on when a change in the bone is to be regarded as a fracture and how this is to be diagnosed.
Various methods and radiographic systems for the detection of vertebral fractures and for risk assessment have already been proposed in the past. Many vertebral fractures are however still not being diagnosed. Even if they are diagnosed, the diagnosis is often not passed on. And an existing diagnosis is not taken into consideration in all cases with regard to the treatment of the patients.
Apart from using 2D X-ray absorption measurements (DXA), bone density measurements are normally carried out using 3D measurements of the bone mineral density (BMD) by means of quantitative CT (QCT) or dual-energy CT. To this end, a measurement region (region of interest, ROI) within the vertebral bodies is set manually by the user or semi-automatically. The CT data from the ROI is then evaluated in order to obtain data relevant to the density determination such as the average HU value or the bone mineral density. Either a calibration dummy or the dual-energy information can be used for the latter.
In order to determine the degree of compression of the vertebral bodies and the risk of a fracture, the height of the vertebral bodies is usually measured manually. Genant et al. (Genant, Wu, van Kuijk, Nevitt, Bone Miner Res, 1993, 8, 1137-48) have presented a semi-quantitative method by means of which the degree of degeneration of the vertebral bodies can be categorized from measuring the height of the vertebral bodies.
Fractures are accompanied by a change in shape of the vertebral bodies, in particular the loss of parallelism of the endplates, breaks or cracks in the external bone structure (cortical bone) and usually a reduced anterior, middle or posterior height. With the method, one speaks of a fracture when the loss in height exceeds 20% of the original height.
The degree of the height loss determines the associated grade of the vertebral fracture. Fractures are categorized as wedge fracture, biconcave fracture or compression fracture, depending on whether the height loss is greatest in the anterior, middle or posterior region of the vertebral body.
The method of Genant et al. is often considered to be the best method for the determination of vertebral fractures on account of the good reproducibility thereof. With this method, vertebral fractures can be well differentiated from other types of deformation. In particular, this method delivers useful information regarding the severity of the fractures and delivers prognoses for their further development.
Siemens AG presented a method for the segmentation of vertebral bodies in a publication in 2013.
US 2012/0183193 A1 shows a method which can be used to automatically detect vertebral fractures. The assessment of the fractures is however carried out manually with this method, which can be extremely time-consuming.
US 2014/0219548 A1 presents a machine learning algorithm which can evaluate 3D images with the aid of geometric structures (landmarks).
EP 2 562 690 A2 presents a method which can be used to compare a measured data set with a reference data set with the aid of random forest decision trees inter alia.
Even though a number of methods therefore exist for the detection of vertebral fractures, the detection of vertebral fractures and the risk assessment remain error-prone, in particular in the case of semi-automatic methods. The detection of very slight fractures is particularly difficult and is recognized only in approximately half of cases.